Description of the Prior Art
This invention relates to a submarine propulsion control system and specifically but not exclusively to a submarine propulsion control system for an expendable unmanned underwater vehicle.
In attempting to dispose of underwater mines it has been usual to place an explosive charge adjacent the mine and then detonate the explosive charge hoping that this will cause sympathetic detonation of the mines warhead, destroying the mine, or at least render the mines sensor and triggering mechanisms inoperative, rendering the mine harmless. Placement of such charges has been carried out by a human diver or by a remote controlled submersible.
Both of these methods have drawbacks. The main drawback is the high risk to the diver or submersible and it is in fact due to the unacceptably high risk to the diver that submersibles are used. However the very high cost of a submersible able to carry an explosive charge to a mine location, deploy the charge adjacent the mine, and return to the mother ship makes loss of the submersible unacceptable, in addition the weight and bulk of the submersible is such that only a very limited number can be stowed aboard a warship and as a result the vehicles mine sweeping capability could rapidly be lost due to destruction of the submersibles. A further disadvantage is that the time taken to dispose of a mine is by these conventional methods is quite long due to the need to get the diver or submersible to a safe distance before detonating the charge and the need for the diver or submersible to return to the mother ship, which must always remain at a safe distance from the mine throughout the operation, to pick up further explosive charges. Since the combined explosive effect of the mine warhead and the disposal charge may be very great the safe distance is relatively large.
It has been proposed to overcome these drawbacks by employing an expendable remotely controlled submersible containing an explosive charge and simply moving the submersible into close proximity to a mine and detonating the charge, destroying the submersible and hopefully detonating the mine warhead or disabling the mine sensor and detonation mechanisms simultaneously. The bulk and expense of such an expendable submersible can be very much less than that of a conventional reusable submersible since there is no need to include any explosive charge deployment mechanism, the range and operational life need only be sufficient for a one way trip to the target mine and all of the control and power systems can be `one shot` devices.
In designing such an expendable submersible it has proved difficult to make the submersible easily and accurately controllable so as to ensure that it can be got into close proximity to the target mine before detonation while simultaneously keeping the submersible cheap and light so as to allow a large number to be carried aboard the mother ship and to allow large numbers to be purchased, the arrangement of motors and propellers to provide forward thrust and the necessary control surfaces to allow controlled horizontal and vertical movement of the submersible has proved particularly difficult.
UK Patent Application Publication Number GB 2281538 attempts to solve the above mentioned problems. This earlier patent application discloses two embodiments, each comprising an unmanned underwater vehicle, cylindrical in shape, propelled by two propellers mounted on arms on either side of the cylindrical body. In both embodiments the arms can be rotated such that the propellers can either be faced in a forward direction, in order to propel the vehicle forwards, or in a vertical direction such as to raise or lower the vehicle, the vehicle having a negative buoyancy.
In one embodiment disclosed in GB 2281538 the arms on which the thrust units are mounted are biased by a spring to a position whereby thrust is generated in a vertical direction. At higher levels of thrust the spring bias is overcome by the force on the arms and these pivot to a position where the thrust is directed in a rearward direction propelling the vehicle forward. In a second embodiment the direction of the thrust units is changed from vertical to horizontal by a transducer within the hull of the vehicle which rotates a shaft through 90.degree. on which the arms are mounted.
The two embodiments disclosed in GB 2281538, described above, are adequate for carrying a warhead into close proximity to a mine to be destroyed, where detonation of the warhead in close proximity to the mine destroys the mine by a sympathetic detonation occurring within the mine. However, more recently, mines have employed new explosive materials such as plastics explosive which are not susceptible to sympathetic detonation. In order to destroy such mines it is desirable to be able to accurately position a shaped charge adjacent the mine such that the blast from the shaped charge is actually focused within the mine to be destroyed. Another advantage of using a directional shaped charge is that even if used against a conventional mine a smaller charge can be used than would be required to ensure a sympathetic detonation and therefore the size of the vehicle carrying the charge can be reduced. This results in a cheaper mine destruction vehicle and also enables more vehicles to be carried by mine clearance vessels. It may also enable the vehicle to be small enough to be deployed from a helicopter.
In order to correctly position a shaped charge relative to a mine to be exploded, it is necessary not only to pilot the vehicle into close proximity to the mine but also to be able to fully control the manoeuvrability of that vehicle when it reaches the mine. It is therefore desirable that such a vehicle be able to perform slow speed manoeuvres whilst substantially in a hover position.